Sofar, several synthetic methods have been reported in the patent literature and in various scientific publications, none of them however enables the direct conversion of esters into ketones in a way which is both economical and technically convenient. The present invention provides a solution to this problem.
The reaction which characterizes the process of the invention consists formally in an anionic splitting promoted by a strong base. To this end, mineral or organic bases such as alkali metal hydrides, alkoxides or hydroxides, preferably sodium or potassium derivatives, are used. Among the said bases one may cite especially sodium or potassium hydride, sodium or potassium tert-butoxide, sodium tert-amylate and sodium methoxide or ethoxide.
The choice among the bases cited above is determined by considerations of economy, safety and occupational health. As a consequence, alkoxides are preferred to hydrides, and among them potassium or sodium tert-butoxide is preferably used.
It could be established that the proportion of the base used must be equal to or higher than the required stoechiometric quantity. In reality, the best yields were achieved by the use of an excess of base.
The reaction times observed are relatively short. Thus at temperatures of about 70.degree. to 80.degree. C., the time of reaction is of the order of 2 to 3 hours when the base used is sodium hydride in a mixture of tetrahydrofuran and phosphorus hexamethyltriamide. Of course, temperature exerts a determining influence on reaction times. The process, which in itself is exothermic, can be carried out at a temperature near the room temperature. Values of between about 20.degree. to 90.degree. C. are preferred. At lower temperatures, the reaction times become too long, whereas at temperatures higher than the above given upper limit, we have observed the formation of unwanted by-products.
As described above, the reaction is effected in an inert organic solvent. Suitable solvents include ethers such as tetrahydrofuran or diisopropyl-ether, amides such as dimethylformamide or phosphorus hexamethyl-triamide. Mixtures of the above cited solvents can also be used. According to a preferred embodiment, potassium tert-butoxide is used as base and dimethylformamide or a mixture of dimethylformamide with tetrahydrofuran can be used as a solvent.